I have run into countless problems in trying to use the Sim900 shield from Itead Studio, version 1.1. I've been talking to one of the engineers at Itead studio in trying to figure my problem out, but to no avail.

I was wondering if there are any UNO users that are using this shield, because I am considering just buying an UNO if it is going to be less of a hassle.

All of the libraries available are written primarily for the UNO anyways, and attempting to use the SoftwareSerial library with the Mega is not working, with the jumpers on the UART multiplexer connected to TX pin 2 and RX pin 3.

Setting the multiplexer to connect directly to the Sim900 module, so that I may access the module through terminal software without uploading anything on the Mega, is also failing. This is the type of responses I get:

Command: AT?Check_protocolno response

And just intermittent messages like the following:

Received SMS from (SIM position: 65534)no response

and so forth. The provider whose SIM card I am using does send an SMS if you insert the SIM card into a new phone, so I assume that is the SMS being picked up, although I'm not entirely sure.

I'd really appreciate to hear from Mega users with the same type of problems, and if there are any UNO users here who can comment on their experience working with this shield.

Right now, I'm using pins 4 and 5 at the UART (already tried 2 and 3) and the switch is at UART_port.The SIM900 library don't allow me to change its pins. And the GSM_Shield library is full of errors. What library did you use? Please tell me how you connected the shield and the arduino. What pins you used in the multiplexer?Thanks in advance.

I'm using a library from iTead Studio, but having the same issues. I have also tried to use the library that you are using, but I also get NO RESP the whole time. You can find it on http://imall.iteadstudio.com/im120417009.html under downloads.

The multiplexer is set to pins 2 and 3. I have tried this using software serial, and also selecting pins 2 and 3 TX/RX and connecting them to the hardware serial ports. No use.

I'm using the IComSat v1.1 with an Uno R3 to send and receive SMS messages.Communication with it is done with SoftwareSerial. My only complaint is that I can't communicate reliably with baud-rate higher than 19200 (I couldn't figure out why this is the case, and simply gave up. 19200 baud is good enough for me).

I didn't use any of the provided software (nor any other available library) because my system must respond to several external events in real-time, and I had to implement a cooperative multi-tasking system, where delay() is never ever ever used.

What I suggest is that before trying to accomplish complicated things like sending SMS, just use a trivial pass-through sketch and see if you can get the SIM900 to response to your AT commands. This is the "hello world" of Arduino to modem connection. When you'll get this right, you'll know that you've got everything configured correctly.

Hey, GOOD news!I had the amazing idea of opening the GSM_Shield.cpp and change all the "mySerial" for "Serial1", and deleting all the #include NewSoftSerialBy doing this, I just changed the comunication to Serial1 (pins 18 and 19) of MEGA, so I jumped the RX to the TX to these pins aaaaaand... the results are the following:

Hey, GOOD news!I had the amazing idea of opening the GSM_Shield.cpp and change all the "mySerial" for "Serial1", and deleting all the #include NewSoftSerialBy doing this, I just changed the comunication to Serial1 (pins 18 and 19) of MEGA, so I jumped the RX to the TX to these pins aaaaaand... the results are the following:

system startupno callno callno call

...And when I called the shield from my cellphone:

incoming voice call from xxxxxxxxx (my number)

YES, it's working!! I'm so happy!! That's it my friends!

Great news!

I've also tried renaming the MySerial instances to Serial1, but I did not remove the #include parts. Definitely going to try this, thanks mate.

I only have to have GSM functionality so the tiny number of pins aren't a problem for me:)